## ← 01-04 What's Important

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Showing Revision 1 created 09/25/2012 by Amara Bot.

1. Astonishingly, the mass of the spacecraft is not important at all.
2. Imagine that you have 2 spacecrafts going along the same trajectory.
3. You could join these to form a spacecraft of twice the mass,
4. and that would still follow the same trajectory.
5. So the mass is of no importance--
6. the mass of the spacecraft, that is.
7. The size of the moon.
8. Well, we should not be hitting the moon,
9. but otherwise the size of the moon is not of importance.
10. The motion of the moon, however, is of vital importance.
11. We have to take care that the rocket is fired into empty space
12. and the moon eventually appears in the right place.
13. The size of the earth is of vital importance
14. to get close to the surface as we return.
15. The motion of the earth around the sun isn't that vital.
16. And should we be treating this as a 3-dimensional problem?
17. Imagine the earth as a sphere and the moon as a sphere,
18. and the trajectory takes us around earth,
19. around the moon and back.
20. This looks very 3 dimensional
21. should we be dealing with xyz coordinates.
22. Actually, however, this trajectory is mostly in a plane.
23. If you look at that motion from above,
24. we see planar motion, and it's almost okay to treat this trajectory in a 2D fashion.